Molecular epidemiology for detecting Norwalk-like viruses in clinical cases and associated environment contamination

Routine monitoring of adenovirus and norovirus within the health care environment

This study investigated the presence of adenovirus and norovirus on ward surfaces using real-time polymerase chain reaction (PCR) to assist in the development of evidence-based infection control policy. Screening was carried out weekly for 6 months in the common areas of 2 pediatric wards. Additionally, a one-off screening was undertaken for adenovirus and norovirus on a day unit and for adenovirus only in patient cubicles while occupied. Over the 6-month screening of common areas, 2.4% of samples were positive for adenovirus or norovirus. In rooms occupied with adenovirus-infected children, all cubicle screening sites and almost all swabs were contaminated with adenovirus. In the day unit, 13% of samples were positive. Cleaning and environmental interaction strategies must therefore be designed to control nosocomial transmission of viruses outside of outbreak scenarios.

Food-borne norovirus-outbreak at a military base, Germany, 2009

BACKGROUND

Norovirus is often transmitted from person-to-person. Transmission may also be food-borne, but only few norovirus outbreak investigations have identified food items as likely vehicles of norovirus transmission through an analytical epidemiological study.During 7-9 January, 2009, 36 persons at a military base in Germany fell ill with acute gastroenteritis. Food from the military base's canteen was suspected as vehicle of infection, norovirus as the pathogen causing the illnesses. An investigation was initiated to describe the outbreak's extent, to verify the pathogen, and to identify modes of transmission and source of infection to prevent further cases.

METHODS

For descriptive analysis, ill persons were defined as members of the military base with acute onset of diarrhoea or vomiting between 24 December 2008, and 3 February 2009, without detection of a pathogen other than norovirus in stools. We conducted a retrospective cohort study within the headquarters company. Cases were military base members with onset of diarrhoea or vomiting during 5-9 January. We collected information on demographics, food items eaten at the canteen and contact to ill persons or vomit, using a self-administered questionnaire. We compared attack rates (AR) in exposed and unexposed persons, using bivariable and multivariable logistic regression modelling. Stool specimens of ill persons and canteen employees, canteen food served during 5-7 January and environmental swabs were investigated by laboratory analysis.

RESULTS

Overall, 101/815 (AR 12.4%) persons fell ill between 24 December 2008 and 3 February 2009. None were canteen employees. Most persons (n = 49) had disease onset during 7-9 January. Ill persons were a median of 22 years old, 92.9% were male. The response for the cohort study was 178/274 (72.1%). Of 27 cases (AR 15.2%), 25 had eaten at the canteen and 21 had consumed salad. Salad consumption on 6 January (aOR: 8.1; 95%CI: 1.5-45.4) and 7 January (aOR: 15.7; 95%CI: 2.2-74.1) were independently associated with increased risk of disease.Norovirus was detected in 8/28 ill persons' and 4/25 canteen employees' stools, 6/55 environmental swabs and 0/33 food items. Sequences were identical in environmental and stool samples (subtype II.4 2006b), except for those of canteen employees. Control measures comprised cohort isolation of symptomatic persons, exclusion of norovirus-positive canteen employees from work and disinfection of the canteen's kitchen.

CONCLUSIONS

Our investigation indicated that consumption of norovirus-contaminated salad caused the peak of the outbreak on 7-9 January. Strict personal hygiene and proper disinfection of environmental surfaces remain crucial to prevent norovirus transmission.

A norovirus outbreak at a long-term-care facility: the role of environmental surface contamination

BACKGROUND

The role of environmental surface contamination in the propagation of norovirus outbreaks is unclear. An outbreak of acute gastroenteritis was reported among residents of a 240-bed veterans long-term-care facility.

OBJECTIVES

To identify the likely mode of transmission, to characterize risk factors for illness, and to evaluate for environmental contamination in this norovirus outbreak.

METHODS

An outbreak investigation was conducted to identify risk factors for illness among residents and employees. Stool and vomitus samples were tested for norovirus by reverse transcription polymerase chain reaction (RT-PCR). Fourteen days after outbreak detection, ongoing cases among the residents prompted environmental surface testing for norovirus by RT-PCR.

RESULTS

One hundred twenty-seven (52%) of 246 residents and 84 (46%) of 181 surveyed employees had gastroenteritis. Case-residents did not differ from non-case-residents by comorbidities, diet, room type, or level of mobility. Index cases were among the nursing staff. Eight of 11 resident stool or vomitus samples tested positive for genogroup II norovirus. The all-cause mortality rate during the month of the outbreak peak was significantly higher than the expected rate. Environmental surface swabs from case-resident rooms, a dining room table, and an elevator button used only by employees were positive for norovirus. Environmental and clinical norovirus sequences were identical.

CONCLUSION

Extensive contamination of environmental surfaces may play a role in prolonged norovirus outbreaks and should be addressed in control interventions.

Calicivirus infections in children

PURPOSE OF REVIEW

Caliciviruses are a major cause of human illness, and are listed as category B pathogens according to the National Institute of Allergy and Infectious Diseases classification of pathogens important for biodefense. Caliciviruses are commonly encountered in contaminated food and water, and a large variety has been implicated as sources of infection during outbreak investigations.

RECENT FINDINGS

New names for two of the four genera of the Caliciviridae were approved in 2002. They are Norovirus, for what were previously called Norwalk-like viruses or small, round-structured viruses, and Sapovirus, for what were previously called Sapporo-like viruses. Caliciviruses are highly diverse genetically and antigenically. This diversity complicates the design of diagnostic assays, yet can be used to discriminate contaminating and infecting strains during outbreak investigations. Of particular interest is the recent finding of naturally occurring recombinant Norovirus strains, all of which have been virulent and are widely dispersed and apparently ecologically indistinguishable from other calicivirus strains. This finding is considered in light of the evidence for recombination between caliciviruses and picornaviruses, and recombination as a more general phenomenon for virus evolution.

SUMMARY

Continued investigations of calicivirus outbreaks are now focusing on the implicated sources of infection. While many foods and environmental waters have long been implicated as outbreak sources, the methods for detecting caliciviruses are being developed and refined. Recognition is now turning to unexpected sources of contamination, such as presumably clean foods and waters, including bottled water and minimally handled foods. Parallels between Norovirus and Salmonella ecology and epidemiology are noted, as a guide to understanding evolving new information about caliciviruses.